1. The problem asks to find an expression equivalent to $x^2 - 81$. 2. Recognize that $x^2 - 81$ is a difference of squares, which follows the formula: $$a^2 - b^2 = (a + b)(a - b)$$ where $a = x$ and $b = 9$ because $81 = 9^2$. 3. Applying the formula: $$x^2 - 81 = (x + 9)(x - 9)$$ 4. Check the other options: - $(x - 9)(x - 9) = (x - 9)^2 = x^2 - 18x + 81$, which is not equivalent. - $(x + 9)(x + 3) - 3$ is not a factorization of $x^2 - 81$. 5. Therefore, the equivalent expression is $(x + 9)(x - 9)$. Final answer: $(x + 9)(x - 9)$